During operation of a compressor in a refrigeration cycle, the compressor is driven by a shaft which is rotated by an electric motor. Simply stated, heat is generated by the motor as electrical current is passed through a series of windings forming a stator, in sequence, which then causes a rotor to rotate. The rotor and stator are contained within a motor housing. The rotor includes a shaft that may be connected to other equipment, which in this case is the compressor. In advanced compressors, the rotor may be supported by electromagnetic bearings. These bearings also may generate heat and the bearings may be considered to be part of the motor. Cooling must be provided to remove heat and prevent the motor from overheating, as motors are usually provided with automatic shut-down features if the temperature of the motor exceeds a predetermined limit in order to prevent damage to the motor.
Various schemes have been used to remove heat from the compressor motor in refrigerant applications. One such technique is described in U.S. Pat. No. 8,021,127 to De Larminat issued on Sep. 20, 2011, (“the '127 Patent”) and assigned to the Assignee of the present invention. The '127 Patent draws refrigerant gas from the evaporator and routes the gas through the motor, the gas passing through the gap between the rotor and the stator. The refrigerant gas from the evaporator is significantly cooler than the temperature of the motor, so the refrigerant gas cools the region as the gas flows through the rotor. After the refrigerant passes through the rotor, it is cycled back to the compressor inlet or suction. Other techniques also pass refrigerant fluid through passageways in the stator. One of the problems with these arrangements is that, while the refrigerant is effective in cooling the motor, the motor can become so cool that condensation forms on the motor housing, undesirably causing water from the condensation to drip from the housing onto the floor.
What is needed is a design that provides cooling to the motor, but which can regulate the temperature of the motor so that the temperature does not fall below the dew point of the air in the location in which the compressor motor is located, thereby preventing condensation from forming on the motor housing and eliminating the problem with water forming on the floor below the compressor motor.